CSIR NET Life Sciences Cellular Organization Syllabus

What signal targets enzymes to the lysosome and where is it added?

Mannose-6-phosphate (M6P), added in the cis-Golgi; M6P receptors in the trans-Golgi network sort the enzymes into clathrin-coated vesicles destined for lysosomes.

What is the resting membrane potential and roughly what value does a typical neuron have?

The voltage difference across the membrane at rest (inside negative), about -70 mV in a typical neuron, set mainly by K+ permeability and the Na+/K+ pump.

State the Nernst equation purpose and write it for an ion at 37°C.

It gives the equilibrium potential of a single ion. E_ion = (61.5/z) log([ion]out/[ion]in) mV at 37°C, where z is the ion's charge.

What does the Goldman-Hodgkin-Katz equation calculate?

The resting membrane potential accounting for the relative permeabilities and concentrations of multiple ions (mainly K+, Na+, Cl-) simultaneously.

What is the chemical composition of the plant cell wall vs the bacterial cell wall?

Plant cell wall: cellulose microfibrils with hemicellulose, pectin, and lignin; bacterial cell wall: peptidoglycan (murein, NAG-NAM chains cross-linked by peptides).

Differentiate Gram-positive and Gram-negative bacterial cell walls.

Gram-positive: thick peptidoglycan layer with teichoic acids, no outer membrane (stains purple); Gram-negative: thin peptidoglycan with an outer membrane containing LPS (stains pink).

Describe the structure of the nuclear envelope and nuclear pore complex.

A double membrane continuous with the ER, perforated by nuclear pore complexes (~120 MDa, octagonal) that regulate nucleocytoplasmic transport; inner membrane is lined by the nuclear lamina (lamins).

What is the function of the nucleolus?

It is the site of rRNA synthesis (transcription of rDNA) and assembly of ribosomal subunits; it forms around nucleolar organizer regions (NORs).

Describe the structure of the mitochondrion and the function of cristae.

A double-membrane organelle: smooth outer membrane and folded inner membrane (cristae) enclosing the matrix; cristae increase surface area for the electron transport chain and ATP synthase (oxidative phosphorylation).

What is the endosymbiotic theory and what evidence supports it for mitochondria/chloroplasts?

Mitochondria and chloroplasts evolved from engulfed free-living prokaryotes. Evidence: own circular DNA, 70S ribosomes, double membranes, binary fission, and sensitivity to bacterial antibiotics.

What are the cis, medial, and trans faces of the Golgi apparatus?

The cis face (entry, near ER) receives vesicles; the medial cisternae process them; the trans face (exit, trans-Golgi network) sorts and packages products for secretion/lysosomes.

List the main functions of the Golgi apparatus.

Post-translational modification (glycosylation, sulfation, phosphorylation), sorting, packaging, and secretion of proteins/lipids; synthesis of certain polysaccharides; forms lysosomes.

What is the function of lysosomes and what enzymes do they contain?

They are membrane-bound digestive organelles with acid hydrolases (active at pH ~5, maintained by V-type H+ ATPase) that degrade macromolecules via autophagy, phagocytosis, and endocytosis.

Differentiate rough ER and smooth ER functions.

Rough ER (ribosome-studded): synthesis, folding, and modification of secretory/membrane proteins. Smooth ER: lipid and steroid synthesis, detoxification, and Ca2+ storage.

What are peroxisomes and which key enzymes do they contain?

Single-membrane organelles for oxidative reactions; contain oxidases (produce H2O2) and catalase (breaks down H2O2); carry out fatty acid beta-oxidation (very long chains) and, in plants, the glyoxylate cycle.

What are the three main types of plastids and their roles?

Chloroplasts (photosynthesis, contain chlorophyll), chromoplasts (store carotenoid pigments), and leucoplasts (colorless storage, e.g., amyloplasts store starch). All derive from proplastids.

What is the function of the central vacuole in plant cells?

Maintains turgor pressure, stores water, ions, and metabolites, sequesters waste/toxins, and contributes to cell enlargement; bounded by the tonoplast membrane.

Describe the internal structure of the chloroplast.

Double membrane enclosing the stroma, which contains thylakoids (flattened sacs) stacked into grana connected by stromal lamellae; thylakoid membranes house the light reactions, stroma houses the Calvin cycle.

Name the three types of cytoskeletal filaments and their approximate diameters.

Microfilaments (actin, ~7 nm), intermediate filaments (~10 nm), and microtubules (tubulin, ~25 nm).

What are the motor proteins associated with actin and with microtubules?

Myosin moves along actin filaments; kinesin (mostly toward + end/anterograde) and dynein (toward - end/retrograde) move along microtubules.

Describe the axoneme structure of cilia and flagella.

A '9+2' arrangement: nine outer doublet microtubules surrounding two central singlets; dynein arms between doublets generate sliding/bending for motility.

Define an operon and name its key components.

A cluster of co-regulated genes transcribed as one mRNA under a single promoter. Components: promoter, operator, structural genes, and (for the regulatory protein) a separate regulatory gene.

Differentiate inducible and repressible operons using lac and trp.

The lac operon is inducible (normally off, turned on by lactose/allolactose inactivating the repressor); the trp operon is repressible (normally on, turned off when tryptophan acts as corepressor).

Differentiate unique (single-copy) and repetitive DNA.

Unique DNA occurs once or a few times per genome (most protein-coding genes); repetitive DNA occurs in many copies, including highly repetitive (satellite, tandem) and moderately repetitive (rRNA genes, transposons) sequences.

What are interrupted (split) genes and the segments they contain?

Eukaryotic genes whose coding sequences (exons) are interrupted by non-coding intervening sequences (introns); introns are removed by splicing during mRNA maturation.

What is a gene family? Give an example.

A group of genes derived from a common ancestral gene by duplication, sharing sequence similarity and often related functions; e.g., the globin gene family (alpha/beta hemoglobins, myoglobin).

Describe the levels of chromatin packaging from DNA to chromosome.

DNA + histones form nucleosomes (10 nm 'beads-on-a-string'), which coil into the 30 nm fiber, then form looped domains on a scaffold, condensing into the metaphase chromosome.

Differentiate euchromatin and heterochromatin.

Euchromatin is loosely packed, gene-rich, and transcriptionally active; heterochromatin is densely packed, gene-poor, and transcriptionally inactive (constitutive at centromeres/telomeres, or facultative).

What are the key differences between mitosis and meiosis in outcome?

Mitosis: one division, 2 diploid daughter cells genetically identical to the parent. Meiosis: two divisions, 4 haploid genetically diverse cells (with recombination and independent assortment).

What unique events occur in prophase I of meiosis?

Homologous chromosomes pair (synapsis) forming bivalents/tetrads held by the synaptonemal complex, and crossing over (recombination) occurs at chiasmata.

List the phases of the eukaryotic cell cycle in order.

G1 (growth), S (DNA synthesis/replication), G2 (growth, prep for division), and M (mitosis + cytokinesis); non-dividing cells exit into G0.

What molecules drive cell cycle progression and at which checkpoints?

Cyclin-CDK complexes drive progression; checkpoints are G1/S (restriction point, DNA damage), G2/M (DNA replication/damage), and the spindle assembly checkpoint at metaphase (M).

What triggers the metaphase-to-anaphase transition?

The Anaphase-Promoting Complex (APC/C) ubiquitinates securin (and cyclin B) for degradation, freeing separase to cleave cohesin so sister chromatids separate.